Candid and Informal Photos
For truly candid or informal pictures, there isn't much setup involved. Makeup and clothing isn't controllable, posing, framing, and lighting are chancy, and so your results will vary wildly. Try not to use any zoom, and be as close to your subject as possible. Make sure your camera's flash is on and set to the proper light source, and focus as fast as you can. That's pretty much all you can do.
Most informal photos are not as spur of the moment as they seem, but are actually portrait photos taken in natural surroundings, using a variant of the ingenue pose. The subjects are using all those turns and twists of the body to appear relaxed and pretty, but they're also looking at *anything* but the camera. In many cases, more setup and hard work goes into informal photos than traditional portrait photos. Flip through a clothing catalog and see what the models are doing - while most people are trying to achieve this look with their informal pictures, a close look will show you just how carefully these shots are put together.
Since most amatuer photographers don't have the kind of equipment needed for outdoor shoots (or want to lug it around!), natural light is the only dependable source. Unfortunately for cameras, the sun moves constantly, requiring the photographer to change everything every twenty minutes or so.
The photographer should always have the sun at their back, and carefully frame the shot to exclude any shiny object. Reflected light, if bright enough, will cause those sunspots on the photo which can obscure the subject, or just marr the picture. Regular carmeras can cut this down by using a polarizing lens filter, which can be puchased in a camera store like Wolf Camera, but digital camera users are out of luck unless they have a built in compensator. Read that manual!
Your subject should be standing in the sunlight, but direct light causes some problems. Your subject may be washed out, or be unable to keep his or her eyes open long enough to take a picture. You can only have so many squinty pictures before your photographer privileges are taken away. A large white umbrella is fantastic here... have a third person stand just behind you, holding the open umbrella high enough to block the sun from your subject's eyes. Try to arrange any shadow from the umbrella to fall completely over your subject's face, so you don't create odd shadows. With luck, the white umbrella will cut the glare without detracting from the amount of light. You can also try having the subject hold the umbrella, just high enough to keep the sun out without obscuring the face *or* creating too much shadow.
Cupping the umbrella behind the subject is another good trick... held at the right angle, the sun will be out of your subject's eyes without looking like a sunshield, and the white cloth will also reflect back a little light for an ambient glow.
If the day is even a little overcast, make sure you use your flash on the appropriate setting. It's amazing how dark a few clouds make your pictures... but a little haze brings out some beautiful colors. Pictures taken right before a good rain are often full of lush color, more than the same picture taken just after the rainfall.
Early morning is the best time to get shots that look fresh and crisp, since the light is softer and the dew creates a soft haze around your subject. Depending on the time of the year, of course, pictures taken after about ten a.m. will loose this cleanliness. From ten or so to about four p.m., photos usually have a warmer, more lived-in look, and as the sun starts to set your pictures will range from golden to a sort of used feel. Sunset photos always feel sad to me, while sunrise shots seem hopeful.
If you're trying to create a fairy tale fantasy feeling, take your pictures just as the sun starts to rise on a day with rain forcast for the late morning. The soft, clean light reacts beautifully with the haze.